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G. E. Ciolek (Rensselaer Polytechnic Inst.), S. Basu (CITA)
We present the results of a numerical simulation modeling the formation and infall of the L1544 protostellar core, which has been the subject of several recent detailed, high-resolution surveys. The parent molecular cloud in which the core forms is modeled as an isothermal, self-gravitating, magnetically supported axisymmetric disk.
Core formation and contraction in the inner magnetic flux tubes of the cloud takes place as a result of ambipolar diffusion, which is the gravitationally-induced drift of neutral matter with respect to ions and magnetic field, due to imperfect collisional coupling between ions and neutrals in a weakly ionized gas. As exhibited in previously published models, the early evolution of the model cloud is quasistatic, with the contraction of the neutrals entirely a result of ambipolar diffusion. After the mass-to-flux ratio in the central flux tubes becomes greater than the critical value for gravitational collapse, the core begins to collapse dynamically, and separation between the supercritical core and the magnetically subcritical envelope ensues. The L1544 core is identified as a recently formed supercritical region.
We compare our results to recent maps of the mass, density, and velocity distribution in L1544. The theoretical predictions are shown to be in very good agreement with the recent surveys (Tafalla et al. 1998, ApJ, 504, 900; Williams et al. 1999, ApJ, 513, L61) and indicate that the infall and evolution displayed in L1544 is highly consistent with ambipolar diffusion models of the formation and collapse of protostellar cores in magnetically supported interstellar molecular clouds.
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